oa.ctrl.rf.fractionExtendAndReduce = {
/**
 * Evaluate the user's answers for a fractionExtendAndReduce
 * 
 * @author Linda Eckardt
 * 
 * @param {array} answer The user's answer
 */
  evaluate: function( answer) {
  var result = [],
      correct = oa.currentProblem.getCorrectAnswer();

  correct = correct[0] / correct[1];
  
  for (var i = 0; i < answer.length; i++)
    if (answer[i][0] / answer[i][1] !== correct)
      result.push(i); // return false positions -> empty array <==> everything correct
  
  if (result.length == 0) {
    oa.view.showSmilingAri();
    if (oa.attemptCounter <= 1)
      oa.correctAnswerCounter += 1;
  } else {
    oa.view.showDisappointedAri();
    oa.attemptCounter += 1;
  }
  percentageCorrect = (oa.learningUnitProblemCounter<=0) ? 0 : Math.floor( oa.correctAnswerCounter / oa.learningUnitProblemCounter * 100);
  oa.view.showPercentageCorrect( percentageCorrect);   
  return result;
}
};